Supplementary blow-out means for high-speed d.c. switches



Jan. 26, 1960 H. FEHLING SUPPLEMENTARY BLOW- Filed Nov. 4, 1957 2,922,926 OUT MEANS FOR HIGH-SPEED D.C. SWITCHES L L NI 2 Sheets-Sheet l I 5 f bar/ward res I current flrrewtort' HE/NZ FEHLING l4 ATTORN EYS Jan. 26, 1960 H. FEHLING 2,922,926

OUT MEANS FOR HIGH-SPEED D.C. SWITCHES 2 Sheets-Sheet 2 Fig.5.

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a z -i lm errzon' HE lNZ FEHLING ATTORNEYS United States 11am Heinz Fehling, Neumunster, Germany, .assignor to Licentia Patent-Verwaltungs-G.m.b.H., Hamburg, Germany Application November 4, 1957, Serial No. 694,361 I Claims priority, application Germany November '5, 1956 5 Claims. or. 317 '11 The present invention relates to high-speed D.C. current switches. More in particular, the present invention relates to a supplementary blow-out arrangement for extinguishing the arcs formed in high-speed D.C. current switches the contacts of which are separated in the substantially currentless period. r

'It is well known that an electrical arc is formed whenever the contacts of circuit-breaking devices are separated and it is therefore well known'to equip switches, and particularly high-speed switches with are extinguishing means comprising a current dependent magnetic blowout means driving the are into an arc extinction chamber of the switch. These magnetic blow-out means influence the electric discharge sectionoccupied by thearc in such a manner that the arc is elongated and cooled and the suificiently elevated voltage gradient is reached which is necessary for extinguishing the arc.

Since the arc tends to keep the circuit alive contrary to the desired breaking of the same by a separation of the contacts of the switch, a speedy and efficient extinction of the arc is particularly important where -a breaking of the circuit must be eifected in a very short time.

Such high-speed switches are, for instance, 'used-asa protective device against backward current in-rectifier units working in parallel. Such rectifier units'consisting of contact transformers are widely used in large scale electrolyses plants and are described, for example,-'in

F. Koppelrnann: Der Kontaktgleichrichter der A'.E.G.,

Elektrotechnische Zeitschrift, 1952, pages .224-227. The primary A.C. current is converted into secondary D.C. current and for the protection of the secondary D.C. current a protective device, e.g. a high-speed switch, is employed in the D.C. current circuit. In case one of the transformer units should fail, this protective device is to reduce a backward current in the secondary circuit to a minimum. For that purpose the switch has to operate at very short notice and in an extremely short time.

It is, of course, the aimto entirely eliminate or prevent backward current and to obtain a maximum protection with a minimum of required switching operations.

Therefore reactors are provided in the secondary circuit which are to delay the commutation of the current from forward into backward current as long as possible. I These reactors are arranged in one pole of the D.C. current supply line. They are magnetically saturated and hence inactive as long as they are supplied with the full rated D.C. current. However, if thecurrent changes from forward to backward current, the reactor counteracts by its proper magnetic energy a further change of the current. The reactor comes into operation as soon as the current has come down to 0 or at least very near to 0.

The reactor results in a current loop (hereinafter designated as stage) the duration of which depends 'on the actuating voltage. Depending on the quality of the choke or reactance iron, the reactor takes care of a backward current of several 100 a.

If the contacts of the switch are separated in the substantial currentless interval, the arc is created simultaneously. "Shortly at the end of the stage the unrestrained backward current sets in and reinforces the arc unless the latter has been previously extinguished. Thus, there is only the short period of the stage available for entirely extinguishing the arc. The comparatively small arc must be entirely eliminated before the end of the loop, as otherwise it will be stabilized and even increased by the backward current.

The problem of so extinguishing the arc has not been satisfactorily solved in the art. This is primarily due to the fact that it was not fully and clearly recognized in the art what impeded the speedy and entire extinction of the arc and what must be done in order to eflFect such a fast and total extinction of the arc.

First of all the magnetic force produced by the current flowing through the blow-out coil in the stage has only a small intensity and therefore cannot quickly and wholly extinguish the arc. In addition, there is a pronounced remanence and the magnetic force acts in a direction contrary to the desired direction and, consequently, the arc is driven right into the contacts of the switch instead of into the extinction chamber.

It was also found that the arrangement of thetripping coil used for automatically actuating the switch in response to an increased current parallel to the blow-out. coil is undesirable and prevents a speedy extinction of the are. For reasons set forth in greater detail further below, there is a backward current. arc, while the current of the blow-out is still forwardly directed, and, as aconsequence, the arc is driven intothe contact blades of the switch. a

It is the object of the present invention to provide a method and device for extinguishing the arc in highspeed switches, particularly as used in rectifiers as a protective device, which guarantees a quick and efiicient extinction of the arc and makes possible a quick circuit breaking by the switch.

This object is achieved by the present invention whereby the magnetic field preventing an extinction of the arc is not only compensated but adjusted to assume the requisite direction of magnetic flux thus driving the are away from the contact blades of the switch and assuring its speedy extinction in the substantially currentless stage. This is done by using the magnetic energy produced by the =back-wound choke coil during the change of the current from forward to backward current and producing with this energy an impulse current for reversing the direction of the blow-out field which otherwise would reinforce the arc and would drive the same into the contact blades of the switch.

The reversing step can be carried out by the supplementary blow-out device of the invention comprising a supplementary blow-out magnet which is so arranged relative to the poles of the main, conventional blow-out magnet as to compensate the flux maintained in the latter and thus bring the magnetic blow-out field in the desired direction.

The invention and its advantages are illustrated by the accompanying drawings, in which Figure 1 shows the connection of a known blow-out system with the blow-out coil and the tripping coil being connected in series; Figure 2 is a diagram and shows the current and flux curves for the known connection of Figure 1 as well as the curve of the magnetic flux I res in the device of the present invention as applied to the known device shown in Figure 1; p g

Figure 3 is a diagram showing the connection of a holding magnet high-speed switch with a tripping inductance L connected in series to a blow-out coil;

Figure 4 is a schematic view and shows the 'efliectof the magnetic blow-out field on the arc, with the'lower curves for. the known connection t 0.5 part showing the field acting in the v the upper part showing the field acting in the right direction; 7

Figure shows .the connection of a .known blow-out ,system with the blow-out coil and the tripping coil being wrong direction and I of Figure 5 as Well as v and used for v high speed switch the blow-out coil of which is shunt .cohnfict dwith the tripping coil.

The known high-speed switches are provided with a blow-out coil 1 creating an inductance L which is connected with a tripping coil 2 creating an inductance L L either in series as shown in Figures 1, 3 or in parallel as'shown' in Figures 5, 8. Such high-speed switches are described for example, in H. Fehling Ein neuer Schnellschalter fiir parallel anbeitende Kontaktgleichrichter A.E.G.-Mi tteilungen 1957, number 5 /6.

- Byway of illustration, Figure 3 shows of a high speed switch of the holding magnet type with the tripping coil. 2 connected in series to the blowwout coil '1. and substantially comprising an armature 2.0, a holding magnet 21, a spring 22, and a reactor 6 and wherein] illustrates thecurrent and l an impulse cur.- rent the function of which latter is described further below.

The'blow-out coil 1 and the tripping coil 2 of a high! speed switch can also be connected in parallel as shown in Figures 5, 8.

Accord ing to the present invention, which is equally applicable to switches in which the tripping coil is con.- nected the blow-out coil in series or in parallel, there are provided supplementary blow-out means adapted to compensate the magnetic flux'otherwise tendingto drive th'e arc into the contact blades 14, 15 of the switch (Figure 4) and, in addition, driving the are away from the contact blades. For this purpose, the horseshoeshaped iron core 3 consisting of sheet laminations is provided with split poles 4 and 4:11 the outer legs 4b and 4c of whichbe'ar the supplementary blow-out coil 8 fo rm ing a part of the secondary circuit further comprising a choke coil 6 and a resistance 7 between the choke coil 6 and the supplementary blow-out coil 8. The iron core the connection the current drop in the 'While the tripping 4 concerned comes into play in order to prevent backward current from being fedinto the D0. circuit.

A choke coil 6 can only .delay the commutation from forward to backward current for a brief period by creating a current loop (stage; see Figures 2, and 6).

Figures 2 and 6 show. tlie "deficiency of known highspeed switches which .do not work with the required degree of'spe'erl due to imperfect arc extinction means.

The magnetic force component K (13 see Figures -2 and 4) produced :by the current] flowing through the blow-out coil 1 and the iron core 3 is not-sufliciently strong during the stage period. It is uncapable of extinguishing the arc, for example the arc 16a, quickly and entirely. In addition, there is a strong remanence which acts in the wrong direction, i.e. it virtually drives the arc 16a into the contact blades 14, 15 of the switch, instead of driving the arcaway from the contact blades of the switch into' an extinction chamber.

.A further disadvantage of the blow-out means ofhighspeed D.C. switchesof the type in which the blow-out and thetripping coil are connected in parallel is illustratedin Figure 6. The tripping coil 2 is used for automatically actuatingthe switch in response to an increase in current andit'is extremely sensitive in regard to such an increase in current, whereas the blow-out coil is considerably less. sensitive. Consequently, a change of currentfrom the static current T and J respectively, to zero takes place at difierent speeds of the current drop, the speedin the first instance being dJ /dt and in the second instance dJ /d't.

' coil. 2 carrying a small load and thusbeing less inductive has already backward current, blow-out coil 1 is much smaller because of the higher load carried by the latter and its resulting higher inductivity. (See Figure 6.) The current of the blow-out coil 1 thustends to retain its forfard direction particularly during the stage period. As

- a consequence at the time of separation of the contacts of the switch during the stage period there is a backward current arcwhile the blow-out coil current is 'forwardly directed. (Figures 2 and 6.) The arc, for example the arc 16a, is thus driven into the contact blades 14, 15 of the switch. Thearc 16a is thus shortened and stabilized and after the end of the stage period it receives a comparatively strong backward current (see Figure 4). V

J Thereby the contact blades of the switch are damaged 3 is furthermore equipped with a substantially U-shaped rent J flows through the tripping coil 2 and the current J 'flows through the blow-out coil 1. At the rated cur; rent of the switch the blow-out current J and the predetermined number of windings of the blow-out coil produce the flux through the arc extinguishing system.

This magnetic flux is facilitated and kept free from disturbances by the horseshoe-shaped iron core 3 con: sisting of sheet laminations.

The magnetic fluxat the split poles 4, 4a, 4b, 4c, is reinforced by the movable contact 12 and the arc horn 9.

In case of a dynamic-change of the current, for examplefif a rectifier unit fails, the current changes from' forward .tobackward ,current at a speed depending on the current circuit constant. In this case, the high-speed protective switch with which the present inventionis or, even destroyed and the switching operation cannot be eflfected with the sufficient degree of speed and'accuracy. 3

The above described supplementary blow-out means of the present invention remedies this situation in the following manner: The secondary tapping 13 for obtaining secondary current from the choke coil 6 feed a sec.- ondary current impulse to the blow-out coil 8. (See Figures 7- and 8.) The current impulse can be controlled by the series resistance 7. This secondary current impulse flows through the supplementary blow-out coil 8 and thereby a magnetic flux o is obtained. This magnetic flux follows a direction which is opposite to the directionofthe magnetic flux I in the iron core 3 which is maintained by'the blow-out coil .1 although there is alreadybackward current in the tripping coil'2. Consequently, the magnetic flux I compensates the residual flux Q Thereby the magnetic field. is eliminated which would otherwise drive the arc, e.g. the arc 16a, in the wrong direction and into contact blades 14, 15 (see Figure 4). The are, eg. the are 16 in Figure 4, is driven away from, the contacts and simultaneously an initial blowvout effect is obtained for the are which still carries but a small current.

It will be easily apparent that the supplementary blowout means of the present invention canbe used with advantage in connection with all switching means having It will also be understood that this invention is susceptible to modification in order to adapt it to diiferent usages and conditions, and, accordingly, it is desired to comprehend such modifications Within this invention as tially currentless interval.

2. In a high-speed D.C. switch comprising contact means adapted to be separated in a substantially currentless interval, a choke coil, blow-out coil means and a tripping coil connected in parallel with said blow-out coil, the improvement of supplementary blow-out means comprising a supplementary blow-out coil and a supplemen- 3. In a high-speed D.C. switch comprising contact means adapted to be separated in a substantially currentless interval, a choke coil, an iron core and a blow-out coil adapted to produce a magnetic flux flowing through said iron core and a tripping coil connected in parallel with said blow-out coil, the improvement of said iron core having, in the immediate vicinity of the efiective area of the magnetic field produced by said blow-out coil,

split poles each comprising an inner and an outer leg, supplementary blow-out means comprising a supplementary blow-out coil wound around the outer legs of the split poles of said iron core, and a supplementary iron core associated with said supplementary blow-out coil, means for obtaining secondary current from said choke coil and adapted to feed a secondary current impulse to said supplementary blow-out coil thereby causing the latter to produce a magnetic flux through said supplementary iron core having a direction opposite to the direction of the magnetic flux produced by said blow-out coil means during the substantially currentless interval.

4. The improvement as described in claim 3, further comprising a series resistance adapted to control the current impulse supplied to said supplementary blow-out coil.

5. In a high-speed D.C. switch comprising contact means adapted to be separated in a substantially curseries with said blow-out coil, the improvement of said iron core having, in the immediate vicinity of the effective area of the magnetic field produced by said blowout coil, split poles each comprising an inner and an outer leg, supplementary blow-out means comprising a supplementary blow-out coil wound around the outer legs of the split poles of said iron core, and a supplementary iron core associated with said supplementary blow-out coil, means for obtaining secondary current from said choke coil and adapted to feed a secondary through said supplementary iron core having a direction opposite to the direction of the magnetic flux produced by said blow-out coil means during the substantially currentless interval.

References Cited in the file of this patent UNITED STATES PATENTS 1,220,569 Steen Mar. 27, 1917 2,643,314 Ridgley June 23, 1953 2,813,953 Eaton Nov. 19, 1957 

